Before Alexander came, the site was associated with the Egyptian settlement of Rhakotis on the Mediterranean coast, west of the Nile Delta. Alexander entered Egypt in 332 BCE and founded Alexandria in 331 BCE; the conquest and the foundation should not be treated as the same event. He chose a location that connected Egypt with the Mediterranean and offered room for a new city rather than simply expanding an old inland capital. The architect Dinocrates of Rhodes is traditionally associated with its planned street grid. Ancient accounts surround the foundation with favourable signs and predictions of prosperity, reflecting the importance later generations attached to the moment. Alexandria's growth, however, was the work of rulers, builders, traders and inhabitants over generations, not a complete city raised in a day.

The defining wonder of Alexandria was the Pharos, the lighthouse built on the island of Pharos just offshore, connected to the mainland by a causeway called the Heptastadion, seven stadia long. Associated with Sostratus of Cnidus, it rose in tiers and became a celebrated landmark for ships approaching the city. Its light guided sailors, while its size and reputation placed it among the Seven Wonders of the Ancient World. The harbour it guarded was a marvel of engineering: harbour basins serving a busy maritime city, sheltered by the island and the causeway. Alexandria became the greatest port in the ancient world, the funnel through which the grain of Egypt, the papyrus of the Nile, and the spices of Arabia flowed to feed and supply the Mediterranean.

The heart of Alexandria's glory was the Mouseion, the temple of the Muses, and the Great Library that grew within it. Ptolemy I Soter, the general who seized Egypt after Alexander's death and founded the dynasty that bore his name, established the Mouseion as a centre of learning where scholars lived, dined, and worked together under royal patronage. His son Ptolemy II Philadelphus continued royal support for collecting and scholarship. Ancient accounts describe vast numbers of scrolls, but the collection's exact size cannot be established with confidence. Scholars like Eratosthenes, the geographer who calculated the earth's circumference worked there; Euclid wrote his Elements there; Callimachus compiled the Pinakes, a major bibliographic work; and Herophilus dissected human cadavers to map the anatomy of the brain. The library was not merely a storehouse but a furnace of thought, and Alexandria became the capital of the mind as well as the sea.

The Ptolemies knew that a Greek city could not rule Egypt without the gods of Egypt. Ptolemy I promoted the worship of Serapis, whose cult drew on the Egyptian connection between Osiris and Apis while presenting the god in a form familiar to Greek worshippers. The Serapeum, built on a hill in the city, became a major religious centre, its sanctuary housing a colossal statue of Serapis so vast that it seemed to touch the ceiling. The sanctuary was also associated with a subsidiary library. The god's cult spread widely through the Mediterranean. In the Serapeum, Greek and Egyptian, living and dead, knowledge and faith, were fused into one.

Alexandria's history continued beyond the dynasty that had built its royal institutions. Cleopatra VII, the last ruler of Ptolemaic Egypt, fought to preserve her kingdom against the growing power of Rome. After her defeat and death in 30 BCE, Egypt became a Roman province, but Alexandria remained an important city and port. The fate of its ancient book collections cannot be reduced with confidence to one fire or one final destruction: accounts of warfare, damaged districts and religious conflict belong to different periods and institutions. The Serapeum was destroyed in 391 CE, while earthquakes damaged the Pharos over later centuries. Yet the city itself endured. Its ancient monuments survive in texts, archaeological remains and the memory of a place where royal power, commerce and scholarship met. The city that Alexander founded outlasted both its founding dynasty and many of the wonders that made it famous.